The objective of this research proposal is to study the mechanism of synthesis of DNA complementary to the viral RNA of the RNA Tumor Viruses. Avian Myeloblastosis Virus, Rous Sarcoma Virus and Maloney Murine Leukemia Virus will be studied. The specific aims of this study are to investigate the mechanism of initiation of DNA synthesis by the reverse transcriptase, to investigate the order in which the viral genome is transcribed, and to study the interaction between the reverse transcriptase and the tRNA primer and template-primer complexes. A further objective is to isolate and characterize the primary transcription product. The product will be analyzed for the presence of additional sequences, a capped 5' terminus and a 3' sequence of polyadenylic acid.